Right, they're not exactly reproducible (and real reproducibility is much cooler), but images solve the main use case (having a clearly defined state) almost as well, at a generally much lower cost.

That’s a valid point and I’ll consider this terminology more carefully in the future. I think a better description might be “transportable?” By that I mean that a specific commit to master builds a container one time with a corresponding tag in our registry, so that exact artifact is versioned and stored, and can then be run and rerun forever more, just as it was built. That’s how we promote releases through qa, staging and to prod and ensure we know what we’re releasing. But it doesn’t have much to do with reproducible builds.